The present invention relates, in general, to a vacuum control system for use in connection with a conventional milking system, and more particularly to a control system for regulating vacuum in a milking system both during a milking phase and during a washing phase.
A milking system is one of the most important components on a dairy farm, for it is used more hours per year than any other type of equipment. A key component of a milking system is a vacuum pump which is used to remove air from the milking system pipelines to create a partial vacuum. In a conventional vacuum milking system, the vacuum pump runs at full speed all the time, regardless of air demands, and a vacuum regulator is generally used to regulate the desired vacuum level by admitting external air, as required, when the vacuum level reaches a predetermined setting. The nominal vacuum levels normally used for milking usually are selected to be in the range from 13 to 15 inches of mercury, but vacuum fluctuations can occur in the system, as when a milking unit falls off the cow being milked, or when the system develops an air leak. It is essential that such fluctuations be limited to 0.6 inches of mercury from the nominal value to enable the vacuum system to meet ASAE standards, but this is difficult to achieve, for such incidents can cause an flow in the system to increase by 20 to 50 cu. ft. per minute over what is needed when the system is operating properly. To compensate for such variations, the size of the vacuum pump is selected to provide the desired vacuum level even when there is a large amount of leakage, and vacuum fluctuations are compensated by the vacuum regulator. Thus, for example, a vacuum pump operates at a constant rate sufficient to maintain a predetermined vacuum level in a reservoir even under leakage conditions, and a vacuum regulator connected to the reservoir admits air as required to control the vacuum level.
In such prior systems, if there is an increase in air flow through the milking system, air flow through the vacuum regulator is reduced so that the reservoir maintains the required vacuum level in the milking line. Ideally, in such systems, increases in the air flow in the milking system and should result in decreases in the air flow through the regulator, and these should be about equal to cancel each other and to maintain vacuum equilibrium in the reservoir. The problem with this arrangement is that only a small portion of the vacuum pump capacity is actually needed for milking, with majority of the air flow passing through the regulator. In such arrangements, the capacity of the vacuum pump always exceeds the capacity needed to milk cows or to wash the milking system, and the pump always runs at full speed and full load, regardless of the actual need for vacuum.
A recent improvement over the foregoing conventional system is described in U.S. Pat. No. 5,284,180 which discloses a system for varying the speed of a vacuum pump to maintain the required vacuum level and stability in the system. In this patent, a vacuum level controlling system utilizes a two-level controller combined with an adjustable speed motor drive for the pump. However, the system described in this patent is designed to provide a slow response, adjustable speed drive for a vacuum system for use during milking, and does not provide a specific control system for use during milk pipeline washing.
There is, therefore, a need for an automatic control system for a vacuum pump in a milking system for reducing electrical energy during a milking phase of operation, and to further control the vacuum pump during a milk pipeline washing phase, with both controls being integrated to provide an improved vacuum control system which will meet the needs of modern dairy farms.